Fishing for Answers
A paleontologist looks at the origins of the human body.
Photograph by Ralf-Finn Hestoft
Neil Shubin and Tiktaalik
In 2005, parents and school officials in Dover, Pennsylvania, were locked in a courtroom debate over a school-board mandate that intelligent design be presented as an alternative to evolution in ninth-grade science classes. The judge in the case ultimately ruled in the parents’ favor, deciding that the requirement was unconstitutional. Throughout the trial, paleontologist Neil Shubin, Ph.D. ’87, Bensley professor in the department of organismal biology and anatomy at the University of Chicago, struggled to remain quiet in his office: on his desk lay the bones of a strange flat-headed, fish-cum-crocodile-like creature-with-a-neck that he and colleagues had found the year before while scraping away at ancient rocks in the Canadian Arctic.
Roughly 375 million years old, from the Late Devonian period, the fossilized creature was a genus of the extinct sarcopterygian (lobe-finned) fish that shares several key features with tetrapods (early four-legged animals). In addition to the neck and non-conical head, Tiktaalik roseae, as it was named, boasted expanded ribs and parts of a shoulder, along with webbed fins—inside which were also primitive bones corresponding to an upper arm, forearm, and pieces of a wrist. All are explicitly non-fish features. Shubin and other scientists say Tiktaalik helps bridge the gap in our understanding of what changes occurred as sea animals crept ashore, and plays a critical role in understanding—and proving—human origins.
“During the Dover trial, I couldn’t tell anyone apart from colleagues about our find,” Shubin says now, with a smile: the news was an exclusive, scheduled to be announced in Nature’s April 2006 cover story. Most of the nation’s news media, major publications, and science magazines followed up with articles about Tiktaalik (the word means “large, freshwater fish” in the Inuktitut dialect of Inuit).
Hailed as “the fish that crawled out of the water” and “the missing link,” Tiktaalik is by far the most important discovery of Shubin’s career, which has centered on the evolution of limbed beings. “I’ve devoted my life to this evolutionary biology stuff—I love it,” he exclaims. “I enjoy going to work because it’s fun working with worms, fish, and salamanders. I think it’s beautiful that remedies for the problems we suffer from will be found by seeing pieces of us nestled in the most primitive and humble creatures that live on the earth.”
Photograph courtesy of Neil Shubin
Remains, and a reconstruction of what researchers believe Tiktaalik roseae looked like as it roamed its corner of the earth millions of years ago
His new book, Your Inner Fish, is an infectious exploration of the 3.5-billion-year history of the human body. It traces our organs back to fossils and prehistoric DNA—how our arm and hand bones came from fins; how our teeth first formed as spiky structures in the mouths of tiny, ancient, jawless lamprey-like fish known as conodonts; and how major aspects of our genome are similar to those of worms. Our ability to talk, for example, depends on the larynx, which is composed primarily of cartilage akin to the gill bars in a fish or shark. Even hiccups—a nerve spasm and inhalation, followed almost immediately (35 milliseconds, Shubin writes) by the “hic” sound—are the product of our shared history with fish and tadpoles, respectively. And the process through which teeth first formed in fish—at base, from the interaction between two layers of tissue—is the same process involved in the subsequent development of scales, hairs, feathers, and sweat glands.
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